Email migration from One tenant to another of Microsoft

Question

Need detailed steps to migrate emails which are 40 GB data each and 7 account from one MS Tenant to another, kindly suggest.

Thanks

Answer 1

Hi @R Singh

Thanks for reaching out to the Microsoft Q&A forum.  

Based on my research, I would like to offer some additional insights that may support the response already provided by Q&A Assist. 

To begin, ensure that every user requiring migration has the Cross‑Tenant Migration Add‑On license. This step is essential to make sure the mailbox migration between tenants functions correctly. 

 

The main stages of a cross‑tenant mailbox migration are as follows: 

1/ Create a migration application in the target tenant 

• Grant the app the Mailbox.Migration permission under the Office 365 Exchange Online APIs. 
• Create a new client secret and keep the secret stored securely for later use. 

2/ Grant consent to the application 

• In the target destination, “Grant admin consent” for the app 
• Create a URL that will be used in the source tenant to approve the application and enable mailbox migration. 

Example: "https://login.microsoftonline.com/contoso.onmicrosoft.com/adminconsent?client_id=[application_id_of_the_app_you_just_created]&redirect_uri=https://office.com"

 

3/ Create a migration endpoint and an organization relationship to your destination tenant in the target tenant. 

4/ From the source tenant, approve the migration application using the provided URL, and create a new organization relationship object that points to your target tenant. 

5/ Prepare the target user accounts for migration 

This includes syncing or setting values such as 

• ExchangeGUID 
• ArchiveGUID 
• LegacyExchangeDN (as x500: proxyAddress) 
• UserPrincipalName 
• TargetAddress or ExternalEmailAddress 

After that, assign the appropriate Exchange Online subscription. 

6/ Verify the cross‑tenant migration configuration by running the Test‑MigrationServerAvailability cmdlet against the cross‑tenant migration endpoint that you created in the target tenant, as mentioned by Q&A Assist. 

You can also use the Cross-tenant mailbox migration validation script, which helps identify inconsistencies across objects. This reduces the amount of time required during the initial preparation phase and ensures that the environment is ready for migration. 

7/ Create and start migration batches 

Use New‑MigrationBatch to begin the migration process once validation is complete. 

For a full reference, you can review Microsoft’s official documentation: Cross-tenant mailbox migration - Microsoft 365 Enterprise | Microsoft Learn. It also includes helpful FAQs that explain many common questions during planning and execution. 

I hope this provides additional insight.  If you have any further questions or updates, please feel free to reach out. 

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Answer 2

To migrate emails from one Microsoft 365 tenant to another, especially with large data sizes like 40 GB per account, you can follow these steps:

1. Prepare Source and Target Tenants: Ensure that both the source and target tenants are properly configured for migration. This includes setting up necessary permissions and creating migration endpoints.
2. Create Migration Endpoint: In the target tenant, create a migration endpoint that points to the source tenant. This can be done using PowerShell commands.
3. Prepare User Accounts: Ensure that the user accounts in the target tenant are created and ready for migration. You can use a CSV file to list the email addresses of the users to be migrated.
4. Validate Migration Configuration: Use the Test-MigrationServerAvailability cmdlet to validate the configuration of your migration endpoint. This ensures that the connection between the two tenants is working correctly.
5. Create Migration Batches: Initiate the migration by creating migration batches using PowerShell. You can use the New-MigrationBatch cmdlet to create a batch for the users you want to migrate. For example:

      New-MigrationBatch -Name "BatchName" -SourceEndpoint "YourEndpointName" -CSVData ([System.IO.File]::ReadAllBytes('users.csv')) -Autostart -TargetDeliveryDomain "targetdomain.onmicrosoft.com"
   

6. Monitor Migration: After initiating the migration, monitor the status of the migration batches to ensure that the emails are being transferred successfully. You can check the status using PowerShell or the Exchange admin center.
7. Post-Migration Steps: Once the migration is complete, ensure that the on-premises mail users are updated with the new target addresses. Also, remove any migration endpoints and organization relationships that are no longer needed.
8. User Verification: After migration, have users verify that their emails and data have been successfully migrated to the new tenant.

For detailed information on each step, including commands and configurations, refer to the official Microsoft documentation on cross-tenant mailbox migration.

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References:

• How to migrate mailboxes from one Microsoft 365 or Office 365 organization to another
• Cross-tenant mailbox migration